Stacked base-pair structures of adenine nucleosides stabilized by the formation of hydrogen-bonding network involving the two sugar groups

We have employed a laser desorption technique combined with supersonic-jet cooling for producing base pairs of adenine nucleosides, adenosine (Ado) and N6,N6-dimethyladenosine (DMAdo) under low-temperature conditions. The resulting base pairs are then ionized through resonant two-photon ionization (R2PI) and analyzed by time-of-flight mass spectrometry. It is found that dimers of these adenine nucleosides are stable, especially in the case of DMAdo, with respect to those of the corresponding bases, i.e., adenine and N6,N6-dimethyladenine. Structural analysis of the DMAdo dimer is performed based on the IR-UV double resonance measurements and theoretical calculations. The result demonstrates that the dimer possesses a stacked structure being stabilized by the formation of hydrogen-bonding network involving the two sugar groups. The occurrence of the frequency shift and broadening is explained satisfactorily based on the anharmonic coupling of the OH stretching modes with specific bending modes and low-frequency modes of base and sugar moieties. (C) 2013 Elsevier B.V. All rights reserved.